Pre-production is in full swing for pre-production and it looks like Bay may have made some progress on his location scouting according to an observation from "jamtron". He reports that while driving by Chicago Studio City, he saw a sign for Michael Bay's office indicating that filming may occur at the site and possibly around the city.
Chicago was also one of the cities Bay mentioned he was checking out for the film. As the name suggests, the facility is Chicago, IL and can be used for the movie production with large spaces for set construction and production offices. Recent productions as the site include Prison Break, Wanted and Public Enemies. If the first two movies are any indication, filming on Transformers 3 is likely to being in May or June. Thanks to jamtron for the tip.